The need for a readily-available supply of fluids to combat dehydration during strenuous activity is well-known. When dehydration occurs, the level of water in the body is below the level necessary for normal body function. Chronic dehydration can lead to short-term and long-tern health problems, including kidney damage. To prevent dehydration, it is imperative that water be consumed regularly at intervals frequent enough to replace water lost through elimination, perspiration and respiration.
One of the challenges to remaining effectively hydrated when undertaking activities in remote locations, such as hiking, camping, climbing and backpacking, is the difficulty in acquiring the volume of potable water to remain properly hydrated. When undertaking these activities, the sheer weight of the water that is required to remain properly hydrated is very cumbersome for an individual to carry. Likewise military personnel have difficulties in replenishing the potable water consumed by forward deployed warfighters that have been effectively removed from conventional supply lines.
Consequently it is highly desirable to consume water from a natural freshwater source encountered in a remote location such as rivers, creeks, streams, lakes, and ponds to avoid dehydration. However a freshwater source cannot inherently be assumed potable as a large percentage of such water is microbiologically unfit for human consumption. This is because such sources potentially contain a myriad of harmful microbiological pathogens. Ingestion of these microbiological pathogens such as viruses, bacteria, and protozoa are known to significantly contribute to diarrheal diseases. Hence to remain effectively hydrated in these remote locations, it is imperative to utilize a personal filtration device for treating water to remove these microbiological pathogens.
Treating water in remote locations using a personal filtration device can be highly effective in reducing the risk of waterborne diseases for people who have no other option than to replenish their fluids from a natural freshwater source. These personal filtration devices include a variety of water purification media that utilize a physical-barrier (i.e., size-exclusion) approach to removing microbiological pathogens and include activated carbon block membrane, ceramic membranes, glass fiber membranes, and polymeric flat sheet and hollow fiber membranes. Personal filtration devices with a physical barrier are superior to a halogen-based disinfectant for treating a freshwater source of an unknown water quality. Chemical disinfectants are unable to remove halogen resistant protozoa (e.g., cryptosporidium) without a long dwell time (4 hours or longer) that potentially puts the user at risk of becoming dehydrated while waiting for the water to become safe to drink. Furthermore, the effectiveness of these chemical disinfectants is highly dependent on the concentration of organic carbon arising from natural organic matter and the temperature of the surface water. Additionally, the halogen-based disinfectants decrease the palatability of the treated water (affects both tastes and odor) which has been shown to reduce the water intake by the user. Finally, unlike chemical disinfectants, the use of a physical barrier removes any suspended solids and colloidal particles from the freshwater source being treated.
A typical arrangement for a personal filtration device is one whereby a filter cartridge containing the size-exclusion membrane is in series with a volumetric-displacement-type, hand-operated pump. Any number of different pumping mechanisms can be employed for delivering the fluid from the contaminated water source to the filter cartridge. For example, a moveable piston or plunger pump can be incorporated into the housing of the personal filtration device to offer a hand-held pumping mechanism. Sample personal filtration devices for purifying water in remote locations with a hand-operated pump are disclosed in U.S. Pat. Nos. 5,330,640, 6,010,626, 8,147,685, 8,281,937, 8,557,115 and U.S. Patent Application No. 2010/0170834.
The art teaches the use of hand pumping devices coupled with a variety of proven water filtration media, including ceramic membranes, glass fiber membranes, and polymeric flat sheet and hollow fiber membranes. The current art also indicates that personal filtration devices of this configuration should be operated in a dead-end filtration mode. When using a dead-end filtration technique, all of the fluid passes through the membrane and all particles larger than the pore sizes of the membrane are stopped at its surface. This means that the trapped debris start to build up a “filter cake” on the surface of the membrane which reduces the efficiency of the filtration process. A reduction in the efficiency of the personal filtration device is observed when these devices are used over an extended period of time to treat freshwater sources with high concentrations of suspended solids and/or natural organic matter. Back-flushing the filter, by reversing the flow through the membrane to remove the debris trapped inside the filter housing, can help unclog the filter by removing the filter cake.
One significant disadvantage of prior-art hand pump personal filtration devices is the inability of their membrane surfaces to be easily cleaned after being used to treat a freshwater source that quickly clogs the membrane surface. The art teaches that the personal filtration device must be manually reconfigured in order to initiate the cleaning step to remove the filter cake. Examples of this mentioned in the art include the user disassembling the filter cartridge in the field to expose the clogged membrane surface or altering/reversing the direction of the flow check valve(s) to initiate a back-flushing procedure. Additionally, special tools are often required to be carried in order to clean the membrane surface. For example, cleaning a ceramic filter is often achieved by using a scouring pad to manually abrade the surface of the ceramic membrane. Furthermore, the user must be careful to only undertake this cleaning step using known potable water to avoid contaminating the clean side (downstream) of the filter cartridge with any microbiological pathogens.
The art indicates that semi-permeable hollow fiber membranes are an effective physical barrier for removing microbiological pathogens since they provide a very high membrane surface per unit volume of the filter cartridge. Consequently, the use of a hollow fiber membrane enables the personal filtration device to have a lighter and more compact (size-efficient) design for the same water production than if the filter cartridge was fabricated from other types of physical barrier materials used in the construction of personal filtration devices.
When compared to ceramic membranes, one of the key performance limitations of using hollow fiber membranes is that it is difficult to completely remove the filter cake from the membrane surface. Ceramic membranes were designed to be cleaned using a mechanical abrasion approach that fully removes the filter cake from the membrane surface but this cleaning procedure cannot be replicated on the more fragile hollow fiber membranes. This means that personal filtration devices with a hollow fiber cartridge can only be cleaned by altering the flow path through the filter cartridge. Furthermore, it is not always possible for visual inspection of the condition of the hollow fiber membrane to determine the extent of the filter cake deposited on the membrane's surface. Therefore, the cleaning step could potentially be initiated at a point where the back flush process may only be partially effective at restoring the water production capabilities of the filter cartridge due to severe buildup of the filter cake. This problem can be addressed by increasing the size of the hollow fiber filter cartridge to spread the filter cake over a larger membrane surface area but this comes at the expense of making the filter small and compact in size.